The invention relates to gage, absolute and differential pressure measurement by means of a pressure sensor with integral overpressure protection for the transducer diaphragm and joints.
Many useful pressure transducer designs are known. See, for example, U.S. Pat. Nos. 4,295,376; 4,458,537 and overpressures without failure.
A few pressure transducer devices, such as that disclosed in U.S. Pat. No. 3,793,885 to Frick, have successfully included a diaphragm member and cooperating housing which provide integral overpressure protection. The diaphragm of that invention has a peripheral rim and web surrounded flexible circular disc body of a free edge design which, typically, has a flexible disc member (D) to web radial length (L) ratio (D/L) greater than 10, a web radial length to web thickness (t) ratio L/t less than 5 and a rim thickness (T) to web thickness ratio T/t less than 4. The Frick diaphragm is welded between two housing pieces to form a pressure capsule. The shape of the inner surfaces of the housing pieces conform to the curved shape of the deflected Frick diaphragm disc so that they fully support the diaphragm during overpressure conditions. During operation under pressure, the welded joints between the diaphragm rim and housing pieces of the capsule are clamped together. This ensures that they are compressively loaded during operation.
The large size of the Frick device adds weight and cost. Also, its concave curved shape requires some complex machining and assembly procedures since the curved convex shape of the deflected diaphragm can be difficult to accommodate precisely using conventional machining techniques. The size of the Frick device also requires that it be filled with a large volume of silicone oil. This can degrade the temperature performance of this type of device.
Most sensors use other methods to protect the sensor during overpressure. They commonly utilize another mechanical system put in parallel with the sensor to protect it by accepting the majority of the overpressure. Many also need to be externally clamped to compressively preload their joints so that they don't fail. These methods add cost and complexity, degrade performance, and reduce reliability. This invention does not need any such device.